eslint-plugin-proper-tests

ESLint plugin for writing proper tests

Installation

npm install -D eslint-plugin-proper-tests

[!NOTE]
For @typescript-eslint v7 use version ^1.0.0 of this plugin. For @typescript-eslint v8 use version ^2.0.0 of this plugin. For ESLint 9 and flat config use version ^2.1.0 of this plugin.

Usage

Flat configuration format:

With flat configuration, use the flat/recommended shared config in your eslint.config.mjs configuration file:

import pluginProperTests from 'eslint-plugin-proper-tests';

export default [
    {
        ...pluginProperTests.configs['flat/recommended']
    },
]

Run ESLint and enjoy the results.

Or, alternatively, add proper-tests to the plugins section of your eslint.config.mjs configuration file and configure the rules one by one:

import pluginProperTests from 'eslint-plugin-proper-tests';

export default [
    {
        plugins: {
            'proper-tests': pluginProperTests,
        },
        rules: {
            "proper-tests/no-useless-matcher-to-be-defined": "error"
            // other rules...
        }
    },
]

Old configuration format:

With old configuration, use the recommended shared config in your .eslintrc configuration file:

module.exports = {
  "extends": ["plugin:proper-tests/recommended"]
}

and you are good to go. Run ESLint and enjoy the results.

Or, alternatively, add proper-tests to the plugins section of your .eslintrc configuration file:

module.exports = {
  "plugins": ["proper-tests"],
  // ...  
}

and configure the rules one by one:

module.exports = {
  "plugins": ["proper-tests"],
  "rules": {
    "proper-tests/no-useless-matcher-to-be-defined": "error"
  }
}

Power of Types

This plugin uses TypeScript to provide more accurate results. To enable this, you need to configure ESLint to work with TypeScript:

Flat configuration format:

import pluginProperTests from 'eslint-plugin-proper-tests';

export default [
    {
        languageOptions: {
            parserOptions: { project: true },
        },
    },
    // ...
]

Old configuration format:

module.exports = {
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "project": true,
    "tsconfigRootDir": __dirname,
  }
}

If parserOptions is not configured, you will get an error:

Error while loading rule 'proper-tests/no-useless-matcher-to-be-defined': You have used a rule which requires type information, 
but don't have parserOptions set to generate type information for this file

Running rules only on test-related files

The rules provided by this plugin assume that the files they are checking are test-related. This means it's generally not suitable to include them in your top-level configuration as that applies to all files being linted which can include source files.

Flat configuration format:

For eslint.config.mjs configs you can use the following syntax:

import pluginProperTests from 'eslint-plugin-proper-tests';

export default [
    {
        files: ['**/*.test.ts'], // limit rules to test files only
        ...pluginProperTests.configs['flat/recommended']
    },
]

Old configuration format:

For .eslintrc configs you can use overrides to have ESLint apply additional rules to specific files:

module.exports = {
  "extends": ["eslint:recommended"],
  "overrides": [
    {
      "files": ["test/**"],
      "plugins": ["proper-tests"],
      "extends": ["plugin:proper-tests/recommended"],
      "rules": { "proper-tests/no-useless-matcher-to-be-defined": "off" }
    }
  ],
  "rules": {
    "indent": ["error", 2]
  }
}

Shareable configurations

Recommended

This plugin exports a recommended configuration that enforces good testing practices.

Flat configuration format:

To enable this configuration with eslint.config.mjs, use the flat/recommended shared config:

import pluginProperTests from 'eslint-plugin-proper-tests';

export default [
    {
        ...pluginProperTests.configs['flat/recommended']
    },
]

Old configuration format:

To enable this configuration with .eslintrc, use the extends property:

{
  "extends": ["plugin:proper-tests/recommended"]
}

and you are done, no other configuration is needed.

Rules

💼 Configurations enabled in.
☑️ Set in the flat/recommended configuration.
✅ Set in the recommended configuration.

Name	Description	💼
no-long-arrays-in-test-each	Disallow using long arrays with objects inside test.each() or it.each(). Force moving them out of the file.	☑️ ✅
no-mixed-expectation-groups	Disallow mixing expectations for different variables between each other.	☑️ ✅
no-useless-matcher-to-be-defined	Disallow using .toBeDefined() matcher when it is known that variable is always defined.	☑️ ✅
no-useless-matcher-to-be-null	Disallow using .toBeNull() when TypeScript types conflict with it.	☑️ ✅

In order to use the rules powered by TypeScript type-checking, you must be using @typescript-eslint/parser & adjust your eslint config as outlined here.

Related Projects

eslint-plugin-jest

The main plugin to be installed when Jest is used.

https://github.com/jest-community/eslint-plugin-jest